There is a focused ion beam apparatus which processes a predetermined region of a surface of a sample by irradiating the predetermined region of the sample with a focused ion beam while scanning, or observes the surface of the sample by detecting secondary particles generated by irradiation of the focused ion beam.
A liquid metal ion source of the focused ion beam apparatus includes an emitter of which a tip end portion is formed in a needle shape and a surface thereof is wet with a liquid metal. The liquid metal is supplied from a liquid metal supplying source to the tip end portion of the emitter, and a surface thereof is always wet with the liquid metal by appropriately energizing a member (filament, or the like) holding the emitter using heating power. Ions are emitted by a strong electric field generated in the tip end portion of the emitter and an extraction electrode where a voltage is applied. A predetermined energy is applied to the emitted ions by a condenser lens configured with a lens electrode and a ground electrode, and the ions are formed in a beam shape. Further, in the focused ion beam apparatus, conditions of the optical system are adjusted, a beam diameter and an ion current value of the focused ion beam are changed, and thus a desired value is obtained.
As the types of the ions of the liquid metal ion source, gallium (Ga) is practically used. In order to emit Ga ions stably, the emitter needs to be operated in a range of 1 μA to 5 μA of ion emission current. The ions are emitted radially from the tip end portion of the emitter. A half of radiation angle at this time is in a range of 10° to 20°. In addition, in order to use the condenser lens in the subsequent stage of the liquid metal ion source in a state in which aberration is small, a distance between the ion source and the condenser lens needs to shortened as much as possible. However, outer peripheral components of the ions emitted from the liquid metal ion source do not pass through a hole of the condenser lens, and stay on an electrode surface, which causes a defect. Measures thereof are disclosed in Japanese Patent No. 4299074.
Japanese Patent No. 4299074 discloses that a smaller beam diameter can be realized by reducing aberration of the condenser lens when a distance between the extraction electrode and the lens electrode of the condenser lens is set to 6 mm or less. In addition, in a technology disclosed in Japanese Patent No. 4299074, the extraction electrode and each electrode of the condenser lens are irradiated with the emitted ions, and secondary electrons and sputter particles are generated from the extraction electrode and each electrode of the condenser lens by the irradiation, such that operation of the ion source is unstabilized. In the technology disclosed in Japanese Patent No. 4299074, when a voltage of the lens electrode is set to 5 kV or less, energy of the ions with which the lens electrode is irradiated. Accordingly, in the technology disclosed in Japanese Patent No. 4299074, even when the lens electrode is irradiated with the ion beam having small energy, since the sputtering yield is reduced, the number of the sputter particles in the lens electrode can be reduced. Accordingly, in Japanese Patent No. 4299074, it is disclosed that stability of the focused ion beam apparatus can be improved.
In addition, JP-A-2002-251976 discloses a configuration that each electrode of the condenser lens is not irradiated with the emitted ions, the secondary electrons and the sputter particles are not generated from each electrode of the condenser lens, and thus stabilized operation of the ion source.
In the related-art technology disclosed in Japanese Patent No. 4299074, since a distance between the emitter and the lens electrode is reduced by setting a distance between the extraction electrode and the lens electrode to 6 mm or less, accumulation of a sputtering material to the emitter is increased. Thus, even if performance of the focused ion beam apparatus is improved, there is a tendency that a stabilizing time of the ion source is shortened.
In addition, in the technology disclosed in JP-A-2002-251976, a size of a lens hole needs to be sufficiently increased (substantially 10 mm) so that each electrode of the condenser lens is not irradiated with the emitted ions. As such, the strong lens action is less likely to be obtained, control of a beam trajectory is limited, and thus a parallel beam cannot be made.